Method and apparatus for forming an article and an article formed thereby

ABSTRACT

A method for forming an article in which thermoplastics materials are used as the binding agent. Materials ( 21 ) are shredded in a shredder ( 1 ), compressed in a compressing chamber ( 15 ) and moulded in a moulding chamber ( 16, 17, 19, 20, 26, 27 ). The thermoplastics material is heated whilst the material is held under compression and then cooled to bind the material together. In one embodiment superheated steam is supplied via tubes ( 31 ) having apertures there along. In another embodiment superheated steam is supplied via apertures in side walls of the mould ( 58, 59 ). Blocks ( 62, 72 ) formed by the method and apparatus of the invention may find application as construction materials etc. and have good structural, thermal and acoustic properties.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for forming anarticle in which thermoplastics materials are used as the binding agent.The invention also relates to an article formed by the method orapparatus.

BACKGROUND OF THE INVENTION

A major challenge facing developed nations is dealing with the volumesof waste produced. Efforts have been made, in particular, in relation tothe recycling of plastics and paper waste. Approaches to the recyclingof plastics have focused upon processes where plastics are sorted intothe various types and controlled proportions are utilised to producerecycled products.

A report entitled “Assessing the potential for post-use plastics wasterecycling—predicting recovery in 2001 and 2006” produced by theAssociation of Plastics Manufacturers in Europe identified the mainconstraints for improving recycling rates for plastic as:

-   i/ the imbalance between the waste collectable and the potential    end-markets for the recycled plastics-   ii/ the presence of large quantities of mixed plastics waste where    the difficulties and energy consumed in separating into homogenous    fractions and cleaning outweigh the environmental gain of mechanical    recycling.

The report considered there to be an upper limit to potential demand formechanically recycled plastics. This report reflects the common mind setof those in the industry that tightly control sorting is required toproduce a valuable product. It also reflects the commonly heldperception that there is a limited marked for the types of articles thatmay be produced.

In the report “SIRA International (1999). Australian Plastics MaterialsRecycling Survey—Report for Plastics and Chemicals IndustriesAssociation. Canberra, Australia” the major problems facing recyclarswere identified as:

-   -   Separation of difficult plastics    -   Contamination between polymers    -   Contaminated waste    -   Plastics re-processing is highly labour intensive for low        returns    -   Demand is unbalanced with supply    -   Not enough end users    -   Collection and separation

Plastic recyclers currently recycle plastics into seven types asfollows:

-   Code 1: Polyethylene Terephthalate (PET or PETE)-   Code 2: High Density Polyethylene (HOPE)-   Code 3: Vinyl (Polyvinyl Chloride or PVC)-   Code 4: Low Density Polyethylene (LOPE)-   Code 5: Polypropylene (PP)-   Code 6: Polystyrene (PS)-   Code 7: Other

Tightly controlled sorting is expensive and is a significant costcomponent in current recycling processes. Where tightly controlledsorting has been required it has been difficult to produce a marketableproduct economically. The characteristics of many products produced insuch recycling processes have been considered to be inferior.

There has also been a prejudice against the use of polyethylene film inrecycling processes. In “Siegler, T. & Perkins, R. (1999). SortingPlastic Bottles for Recycling. Ascotney, Vermont: DSM EnvironmentalServices for The American Plastics Council” the following points werenoted:

-   “Acceptance of even small amounts of recyclables in plastic bags    will significantly reduce equipment efficiency unless all of the    film is removed with a film removal system at the front end.”and-   “The composition of material delivered to the MRF (materials    recovery facility) has a significant impact on processing    efficiency. Contaminants entering MRFs 5, 6, and 7 represented    between 3.7% and 6.7% of the incoming material. This seemingly small    amount of incoming contamination was responsible for between 31 and    67% of sorting labour at these the MRFs.”and-   “Increased public education is necessary to better inform    participating households which plastic containers are acceptable in    the recycling program.”

Rathje, W and Murphy, C. cite as one of the “Five Major Myths aboutGarbage and Why They're Wrong” that:

-   “The biggest problem faced by recycling is not the technological    process of turning one thing into another. Anything can be    recycled—and would be if demand for what it could be recycled into    were great enough. The key, then, is demand, and demand for many    recyclables is often soft.”

To date the most commercially attractive recycling progresses have beenthose utilising industrial waste. Industrial waste may typically consistof large batches of one type of plastics which avoids the need for anysorting process.

OBJECT AND STATEMENT OF THE INVENTION

It is an object of the present invention to provide a method andapparatus for forming an article from mixed plastics waste whichovercomes these problems or at least provides the public with the usefulchoice.

According to a first aspect to the invention there is thus provided amethod of forming an article comprising the steps of:

-   -   i/ introducing into a chamber material to be formed containing a        sufficient amount of thermoplastics material to bind the        material together;    -   ii/ compressing the material within the chamber so that it        occupies a reduced volume;    -   iii/ generating sufficient steam within the chamber to melt        sufficient thermoplastics material substantially throughout the        material to bind the material together when cooled; and    -   iv/ releasing an article produced from the chamber.

The energy source may be superheated steam, a microwave energy source oren ultrasonic energy source. The material is preferably a mixture ofshredded thermoplastics and other materials. The material is preferablycompressed in a first direction and then in a second directiontransverse to the first direction. The material may be furthercompressed in a third direction transverse to the first and seconddirections. The article formed may either be cooled within the chamberby liquid or air or released into a cooling medium.

According to a further aspect to the invention there is provided amethod of forming an article comprising the steps of:

-   -   i/ introducing into a chamber material to be formed containing a        sufficient amount of thermoplastics material to bind the        material together when cooled;    -   ii/ compressing the material within the chamber so that it        occupies a reduced volume;    -   iii/ introducing sufficient superheated steam into the        receptacle to melt sufficient thermoplastics material to bind        the material together substantially throughout the material; and    -   iv/ releasing an article produced from the chamber.

The material is preferably compressed in a first direction and then in asecond direction transverse to the first direction. The material may befurther compressed in the third direction transverse to the first andsecond directions.

The material is preferably a mixture of shredded thermoplastics andother materials. Superheated steam is preferably introduced into thechamber either by apertures in one or more side of the chamber or viatubes inserted into the chamber when steam is introduced. Thetemperature of the superheated steam is preferably between 200° C. to400° C., more preferably 260° C. to 320° C., most preferably 280° C. to300° C. The pressure maintained within a chamber is preferably between 5to 100 psi, more preferably 5 to 60 psi, most preferably 10 to 20 psi.Superheated steam is preferably introduced into the mould for a periodof between 10 seconds to 5 minutes, preferably 10 to 60 seconds, mostpreferably 10 to 20 seconds. Where the temperature is hold constant atabout 300° C. and supplied for a period of about 15 seconds the pressuremaintained within a chamber is preferably between 5 to 26 psi, morepreferably 5 to 20 psi, most preferably 10 to 15 psi. Where thetemperature of the superheated steam is about 300° C. and the pressureis maintained at about 15 psi the superheated steam is preferablysupplied for a period of between 10 to 16 seconds. The material ispreferably reduced in volume by factor of between 5:1 to 25:1, morepreferably by factor of between 10:1 to 20:1. The material may includeup to 20% non-thermoplastic material, preferably up to 10%non-thermoplastic material.

According to a further aspect to the invention there is provided anarticle forming apparatus including:

-   -   a moulding chamber for receiving and containing compressed        material including thermoplastics material; and    -   outlets for providing superheated steam into the chamber        positioned to provide sufficient heat substantially throughout        the material within the chamber to melt the thermoplastics        substantially throughout the material.

The outlets may be in the form of apertures in one or more face of themoulding chamber or in the form of one or more tube having apertures forproviding a relatively even distribution of superheated steam throughoutthe chamber. The apparatus may include a compressing chamber forcompressing the material prior to moulding. One pair of walls may movetogether in a first direction, a second pair of walls may move togetherin a second direction, transverse to the first direction, and a thirdpair of walls may move together in a third direction transverse to thefirst and second directions. The moulding chamber is preferably definedby the first, second and third pairs of walls when moved together.

According to a further aspect to the invention there is provided anarticle forming apparatus including:

-   -   a compressing chamber for receiving material and compressing it        in at least two transverse directions to a reduced volume; a        moulding chamber for containing the compressed material; and    -   a microwave source for supplying microwave radiation        substantially throughout the moulding chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by the way of example with referenceto the accompanying drawings in which:

FIG. 1: is a schematic diagram of an article forming system according toa first embodiment to the invention.

FIG. 2: is a cross sectional side view of the article forming apparatuswith material to be formed loaded in the compression chamber.

FIG. 3: shows a cross sectional side view of the article formingapparatus after a first stage of compaction.

FIG. 4: shows a front cross sectional view of the article formingapparatus.

FIG. 5: shows a front cross sectional view of the article formingapparatus after a second stage of compression.

FIG. 6: shows a front cross sectional view of the apparatus after athird stage of compression has been performed.

FIG. 7: shows a front cross sectional view of the apparatus when steaminjection tubes have been inserted into the moulding chamber.

FIG. 8: shows a side cross sectional view of the article formingapparatus as shown in FIG. 7.

FIG. 9: shows a side cross sectional view of the article formingapparatus after a moulded article has been ejected.

FIG. 10: shoes a front cross sectional view of the apparatus as shown inFIG. 9.

FIG. 11: shows the hydraulic circuit for the system of FIGS. 1 to 10.

FIGS. 11A and B: show front and side cross sectional views of thehydraulic circuit of the article forming apparatus.

FIG. 12: shows a schematic diagram of a water circuit for the system ofFIGS. 1 to 11.

FIG. 13: shows a front cross sectional view of an article formingapparatus according to a second embodiment.

FIG. 14: shows a side cross sectional view of the article formingapparatus of FIG. 13.

FIG. 15: shows a front cross sectional view of an article formingapparatus according to a third embodiment.

FIG. 16: shows a side cross sectional view of the article formingapparatus of FIG. 15.

FIG. 17: shows an article in the form of a block produced by any one ofthe article forming apparatus of FIGS. 1 to 16.

FIG. 18: shows a wail constructed of blocks of the type shown in FIG.17.

FIG. 19: Shows a cross sectional view of a wall formed using the blocksof FIG. 17.

FIG. 20: Shows a cross sectional view of a wall formed using the blocksof FIG. 17 when threaded onto a road.

FIG. 21: Shows a cross sectional view of a wall formed using the blocksof FIG. 17 when threaded onto a post.

FIG. 22: Shows a cross sectional view of a wall formed using the blocksof FIG. 17 with irrigation means provided.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring firstly to FIG. 1 a schematic diagram of a system for formingan article according to a first embodiment will be described. Materialto be processed is supplied to shredder 1. The material provided toshredder 1 includes a sufficient proportion of thermoplastic material tobind the article together when processed. Preferably, the material iswaste plastic material. Mixed waste plastic material may be provided ina substantially unsorted state. Sorting into plastics types willgenerally not be required for normal mixtures of domestic waste. Somesorting may be desirable to exclude undesirable non plastics materialsincluded within the waste such as large non-plastic items or expandedpolystyrene. Preferably greater than 80% and more preferably greaterthan 90% of the material consists of plastics material.

Shredder 1 preferably shreds the material into strips. A suitableshredder is a PT 45 shredder produced by Peak Technology Limited ofWellington New Zealand. The material is preferably shredded into stripsof between 10 to 20 mm in width, most preferably about 16 mm in width.There will be a certain degree of variation in strip width due to theshredding process and a certain degree of roughness of the edge of theshredded material may be advantageous as discussed later.

As well as plastics materials certain other materials such as sawdust,wood chip, paper or other fibres may be added up to an amount of about20% although preferably less than 10%.

The shredded material is fed by feed-hopper 2 into a washing and dryingdrum 3. An auger 5 is provided along the length of the drum to feedmaterial through the drum as it is rotated. In first stage 4 water issprayed upon the shredded material as it passes through the first stageand auger 5 advances the material through the drum to a perforateddrying section 6. In a second rinse stage 7 the shredded material isagain sprayed with hot water and auger 5 advances the shredded materialthrough section 7 into drying section 8. Prying section 8 has largeperforations which allow water to drain from the shredded material.Residual heat retained by the material after being heated by the hotrinse water facilitates drying of the material. The entire drum 3 isrotated via an hydraulic or an electric motor.

Shredded material from drying section 8 is fed to accumulator 9 and fadby auger or conveyor 10 to article forming apparatus 11. Boller 12provides steam to superheater 13 which provides superheated steam toarticle forming apparatus 11.

Referring now to FIG. 2 a side cross sectional view of an articleforming apparatus according to a first embodiment is shown. Afeed-hopper 14 supplies shredded material to a compressing chamber 15.Compressing chamber 15 consists of three pairs of walls that may bemoved together to compress the material therein. A first pair of walls16 and 17 are shown in FIG. 2. Wall 17 is fixed in this case and wallmay 16 may be moved towards wall 17 upon extension of ram 18. Once ram18 is extended wall 16 moves to the position shown in FIG. 3.

Referring now to FIG. 4 a front cross sectional view of apparatus 11 isshown. In this view side walls 19 and 20 are seen to contain shreddedmaterial 21 there between after walls 16 and 17 have been moved togetherin a second stage of compression rams 22 to 25 are extended to movewalls 19 and 20 to the position shown in FIG. 5. As shown in FIG. 5 theshredded material 21 has undergone compression in a first direction andthen a second direction transverse to the first direction. Moving twowails together in the second compressing stage assists in evening thestock of compressed material.

In a third stage of compression walls 26 and 27 are moved together. Rams28 and 29 are extended to move walls 26 and 27 together to the positionshown in FIG. 6. The material has then undergone compression in a thirddirection transverse to the first and second directions of the priorcompression stages.

Compressing the shredded material in one direction and at least afurther direction transverse to the first direction is considered to beadvantageous. Compressing the material in a single direction can resultin alignment of strips. Compressing the material in transverse directionassists in producing a structure that is less aligned in any singledirection. This process also assists in promoting interlocking of therough edges of strips of material to assist in binding the materialtogether. However, in some applications alignment of the strips could bedesirable in which case compression in single direction could be used.The compressing chamber is preferably vertically elongate to minimisethe footprint of the apparatus and to promote even distribution ofmaterial 21 (i.e. avoid peaking of material in the stack). Compressionis preferably substantially equal in each stage (about 2.5:1 in eachstage). Different densities of block may be formed by filling thecompressing chamber with different weights of material.

After the three stages of compression the three pairs of wells 16 and17, 19 end 20 and 25 and 27 have moved together to define a mouldingchamber containing shredded material 21. Although in this embodiment themoulding chamber is formed as part of the compressing chamber it will beappreciated that a separate moulding chamber and compressing chamber maybe employed.

In the next step of the process sufficient energy must be provided tothe moulding chamber to melt sufficient thermoplastics material withinshredded material 21 so that, upon cooling, the material will besubstantially bound together. Material 21 is saturated with heat energyto ensure a relatively consistent bonded matrix is formed. Polyethyleneis a large component of typical domestic waste and has excellentadhesive properties as utilised in hot glue guns. Low densitypolyethylene is usually a difficult waste for recyclers to deal with andconstitutes a large proportion of residential waste. Polyethylene may bemelted front a crystalline form and upon cooling returns to acrystalline form. It is an effective binding agent in the method of theinvention. Other low melting point thermoplastics may also be utilisedto bind the material together.

In order to achieve an economic process producing a viable product, asufficient amount of energy to melt the binding thermoplastics materialsubstantially throughout the article must be provided within arelatively short time period. According to a first aspect to theinvention superheated steam is introduced via tubes having aperturesalong their length so as to achieve heating of the thermoplasticmaterial throughout the mould to provide effective binding.

Referring now to FIG. 7 the moulding stage according to the first aspectto the invention will be described. In FIG. 7 there is shown a manifold30 having a plurality of tubes 31 extending therefrom. In this exampletubes 31 have an outside diameter of 9.5 mm and a wall thickness ofbetween 0.9 to 1.2 mm. 2 mm apertures are drilled through the tube at 25mm spacings and the end of the tube is closed to form a pointed end.Superheated steam is input to manifold 30 via inlet 32 and output intotubes 31. Tubes 31 are distributed throughout the chamber duringmoulding and are provided with apertures at intervals along their lengthto provide superheated steam at a variety of locations throughout themoulding chamber. As shown in FIG. 7 ram 33 extends to insert tubes 31through apertures in wall 26 into material 21. The moulding chamber issubstantially sealed and the pressure within a chamber can be controlledvia an adjustable relief valve 34. In this example the chamber isdimensioned to form a block of approximately 200 mm by 200 mm by 400 mm.Steam is introduced at a prescribed temperature and pressure for apredetermined period to ensure that the correct amount of energy issupplied to the material 21 at an appropriate rate.

The superheated steam preferably has a temperature within the manifold30 of between 200° C. to 400° C., more preferably 260° C. to 320° C.,most preferably 280° C. to 300° C. The pressure maintained within themoulding chamber is preferably between 5 to 100 psi, more preferably 5to 60 psi and most preferably 10 to 20 psi. The period of supply ofsuperheated steam to the moulding chamber is preferably to 10 sac to 5min, more preferably 10 to 60 sec. most preferably 10 to 20 sec.

The objective is to provide sufficient heat throughout the mould to meltsufficient thermoplastics materials to effectively bind materials 21together on cooling. The heat must be applied at an appropriatetemperature and pressure to avoid degradation of the product and to makethe process economic. Operating parameters will vary depending upon thematerials concerned and the density of product to be formed. Certainpreferred operating parameters have been determined for mixed wasteplastics as follows.

One approach is to maintain temperature and period of supply ofsuperheated steam substantially constant and to vary the pressuremaintained within the moulding chamber. It has been found experimentallythat good quality products can be achieved when the temperature of thesuperheated steam is maintained at about 300° C. and supplied for aperiod of about 15 sec. For a high density block (275 to 350 kg/m³) thepressure is preferably maintained at between 15 to 25 psi. For mediumdensity block (200 to 270 kg/m³) the pressure is preferably maintainedat between to 20 psi. For a low density product (between 100 to 200kg/ma³) the pressure is preferably maintained at between 5 to 15 psi.Different densities of block may be desirable for different applicationssuch as structural blocks, acoustic blocks, thermal insulation etc. Amanifold temperature of about 300° C. is advantageous as it is lowenough not to degrade the material but high enough to deliver energysufficiently quickly. This temperature is easily and economicallyachieved with a superheater. This temperature also allows the pressureto be kept relatively low. Use of a fixed cycle time means that priorand subsequent process steps are not affected by the type of articlebeing produced.

Another approach is to maintain the temperature of the superheated steamconstant at about 300° C. and the pressure constant at about 15 psi. Inthis case the period of supply of steam to the moulding chamber willtypically vary between 10 to 20 sec. This will depend upon the materialsutilised.

Referring again to FIG. 7 it will seen that venting is provided viavariable pressure relief valve 34 at the top of the mould. It ispreferable to provide venting at the top of the mould as the energydistribution from tubes 31 tends to have a pear shape distributiontowards the bottom of the mould. By venting at the top, steam from thebottom travels through the top zone and results in more uniform heatingof all materials in the block.

Once sufficient steam has been supplied to the moulding chamber manifold30 and tubes 31 are retracted by ram 33. After a sufficient quantity ofsuperheated steam has been supplied to a mould cooling water isintroduced Via inlet 35. Any suitable cooling liquid or gas may beutilised although water is preferred. Cooling the article 21 formed inthe mould has the advantage of fixing the article in the shape of themould prior to ejecting it. However, article 21 may be ejected from themould into a cooling fluid.

Upon cooling of article 21 wall 27 may be rotated by ram 36 to allow aformed block 21 to be ejected from the moulding chamber as shown inFIGS. 9 and 10.

Referring now to FIG. 11 an hydraulic circuit for the system of FIGS. 1to 10 is shown. An hydraulic tank 37 supplies hydraulic fluid to anhydraulic power source 38. This supplies hydraulic fluid to drivehydraulic motor 39 which rotates drum 3 Hydraulic power source 38 alsoprovide hydraulic fluid to drive hydraulic motor 41 of conveyor 10.Hydraulic fluid is also supplied from power source 38 to shredder motor42. Hydraulic fluid is returned via return lines (dashed lines) tohydraulic tank 37. Hydraulic power source 38 also provides pressurisedhydraulic fluid to hydraulic controller 40 which supplies fluid to therams of apparatus 11 under the control of programmable logic controller(PLC) 43,

FIGS. 11A and 11B show the hydraulic circuit from hydraulic controller40 to rams 18, 22 to 25, 28 and 29, 33 and 36. These are controlled tooperate in the appropriate sequence by PLC 43.

Referring now to FIG. 12 a water circuit for the system of FIGS. 1 to11B is shown. Clean water is supplied to water tank 44 which supplieswater to hotwell tank 46. Hot water from hotwell tank 45 is supplied towashing tank 46. Washing tank 46 supplies hot water to sprayer 47 forthe first wash of shredded material. Hot water for the second rinse issupplied from hotwell tank 45 to sprayer 48. Excess water from the twodrying stages is collected in drip trays 49 and 50, is filtered byfilters 51 and 52 and pumped by pump 53 back to washing tank 46.Although filtered, the water in washing tank will be of a lower qualitythan the other tanks and is suitable for the first wash cycle.

Water from hotwell tank 45 is also supplied to boiler 54. Boiler 54supplies steam to superheater 55. Superheater 55 supplies superheatedsteam to three way valve 56 which supplies superheated steam to manifold30 of apparatus 11 or to condenser 57 to be returned to hotwell tank 45.Cooling water to cool a moulded article is supplied to inlet 35 fromhotwell tank 45. Water collected from drip tray 58 is returned tohotwell tank 45.

Referring now to FIGS. 13 and 14 an apparatus according to a secondaspect of the invention is shown. In this case a relatively thin articleis to be formed and superheated steam is supplied via side walls of themoulding chamber. The article forming apparatus is identical to theapparatus described above except that top wall 26 and manifold 30 arereplaced by mould portion 58 and wall 27 is replaced by wall 59. In thiscase superheated steam is supplied via inlet 60 to an interior cavity ofmould portion 58. Superheated steam from the interior cavity of mouldportion 58 passes through a number of apertures adjacent the surface ofmould portion 68 opposite material 21. Likewise, wall 59 has a cavitytherein and apertures are provided in the face of wall 69 adjacentmaterial 21 and are distributed so as to provide relatively uniformheating throughout material 21. This method is suitable where relativelythin articles are to be manufactured. Apart from the provision of steamvia apertures rather than tubes operation is as per the embodiment shownin FIGS. 1 to 12,

Referring now to FIGS. 15 and 16 a further alternative embodiment isshown which again is identical to apparatus 11 except that manifold 30and needles 31 have been replaced by a microwave transmitter 61. In thiscase heating energy is supplied to wet material 21 by microwaveradiation rather than through the use of superheated steam. In this caseit is necessary to supply water to the moulding chamber and for thechamber to be sealed so that elevated pressures can be achieved. Watermay be injected into the mould or wet material may be introduced. Themicrowave radiation heats the water to form superheated steam throughoutthe moulding chamber. Operation is otherwise identical to that describedabove. Other energy sources that can heat moisture throughout themoulding chamber may also be employed.

Referring now to FIG. 17 an article in the form of a block formed by theapparatus of the invention is shown. In this case block 62 has recesses63 formed in the one face and corresponding protrusions 64 formed anopposite face. The protrusions 64 may be engaged within correspondingrecesses 63 of adjacent blocks when forming a wall as shown in FIG. 18the protrusions 64 end recesses 63 help to locate blocks and maintainlateral stability. A block may of course be produced not havingprojections or recesses.

Referring now to FIGS. 19 to 22 interengaging projections and recessesare not shown, although they could be employed, in the walls shown inFIG. 19 the wall is built upon a concrete foundation 71 formed on ground70. Blocks 72 are stacked one on top of the other and secured togethervia any suitable adhesive. The blocks may be secured together utilisingan adhesive product, such as a bitumastic material which cures in theatmosphere or glue from a hot glue gun.

In this embodiment the blocks are coated with nutrient and orpropagation material such as seeds. Further, an irrigation tube 74 maybe provided along the top to irrigate the plants growing on the wall.

The blocks 72 may preferably include a certain amount of paper or othermaterial suitable to retain moisture which provide a suitable medium forthe material propagate thereon. Recycled plastics material may provide asuitable porous structure into which the roots of plants may extend toform a natural self supporting structure.

Referring now to FIG. 20 an alternative embodiment is shown in which arod 75 preferably formed of steel, extending from a concrete footing 76is secured in ground 77. A plurality of blocks 72 have longitudinalbores provided therethrough so that blocks 72 may be threaded along aseries of poles 75 provided at intervals. The bores in blocks 72 may beformed in an offset manner so that the blocks may be offset betweenlayers.

FIG. 21 shows a similar embodiment in which a wooden post 78 extendsfrom a concrete foundation 79 and a plurality of blocks 72 are threadedon post 78 through apertures formed therein.

FIG. 22 shows a wall similar in construction to that shown in FIG. 20 inwhich bracelines 80 are utillised to stabilise the wall. The bracelines80 may either extend adjacent blocks 72 or may taper away from theblocks towards the base as shown in the two configurations. Buttressesmay also be provided at intervals along any of the above walls toprovide additional stability.

It will thus be seen that the present invention provides a method andapparatus for producing articles from plastic waste material suitablefor use in construction, insulation, acoustic barriers etc. The methodof the invention enables substantially unsorted plastics waste to beprocessed into viable construction materials. The use of mixed plasticsmaterials without sorting provides significant economies over priormethods. The apparatus of the invention is relatively simple and can beconstructed at relatively low cost. The method of the invention allowsbuilding materials to be produced economically from plastics waste.

Products formed by the method of the invention have good shockresistance and absorption characteristics making them suitable for usein structures prone to earthquakes or vibration. Products formed by themethod of the invention also have good thermal insulation and acousticisolation properties making them suitable for use in certain buildingapplications. The material also has memory and so can return back to itsoriginal shape after deformation.

The present invention is seen as a significant advance in the processingof mixed waste plastics by eliminating the need for sorting plasticsinto individual plastic types.

1. A method of forming an article comprising the steps of: i)introducing into a chamber material to be formed containing a sufficientamount of thermoplastics material to bind the material together; ii)compressing the material within the chamber in one direction and then ina second direction, transverse to the first direction, so that itoccupies a reduced volume; iii) inputting sufficient energy to meltsufficient thermoplastics material substantially throughout the materialto bind the material together when cooled, and iv) releasing an articleproduced from the chamber.
 2. A method as claimed in claim 1 wherein thematerial is subsequently compressed in a third direction transverse tothe first and second directions.
 3. A method as claimed in claim 1,wherein superheated steam is supplied to the chamber from a super heatedsteam source.
 4. A method as claimed in claim 3 wherein the superheatedsteam is supplied through one or more side wall of the chamber.
 5. Amethod as claimed in claim 3 wherein the superheated steam is suppliedvia tubes supplied with superheated steam having apertures along theirlength which are inserted into the chamber in step iii.
 6. A method asclaimed in claim 1 wherein fluid within the chamber is heated by amicrowave energy source to generate steam.
 7. A method as claimed inclaim 6 wherein water is injected into the chamber before microwaveenergy is supplied.
 8. A method as claimed in claim 1 wherein thematerial is shredded prior to being placed within the chamber.
 9. Amethod as claimed in claim 8 where the material is shredded into stripsof about 10 to 20 mm in width.
 10. A method as claim in claim 1 whereinthe thermoplastics material is waste plastics.
 11. A method as claimedin claim 10 wherein the thermoplastics material is a mixture ofdifferent types of waste plastics.
 12. A method as claimed in claim 10wherein the thermoplastics material includes PETE and/or polyethylene.13. A method as claimed in claim 10 wherein the other material to beformed includes at least one of sawdust, wood chips, fibres and papers.14. A method as claimed in claim 1 wherein the article is cooled byintroducing liquid to the chamber prior to release of the article instep iv.
 15. A method as claimed in claim 1 where the article is cooledby introducing air to the chamber prior to release of the article instep iv.
 16. A method as claimed in claim 1 wherein the article iscooled by releasing it from the chamber into a fluid bath.
 17. A methodof forming an article comprising the steps of: i) introducing into achamber material to be formed containing a sufficient amount ofthermoplastic material to bind the material together; ii) compressingthe material within the chamber so that it occupies a reduced volume;iii) introducing sufficient superheated steam into the chamber to meltsufficient thermoplastics material substantially throughout the materialto bind the material together when cooled; and iv) releasing an articleproduced from the chamber.
 18. A method as claimed in claim 17 whereinthe material is compressed in one direction and then in a seconddirection transverse to the first direction.
 19. A method as claimed inclaim 18 wherein the material is subsequently compressed in a thirddirection transverse to the first and second directions.
 20. A method asclaimed in claim 17 wherein the material is shredded prior to beingsupplied to the chamber.
 21. A method as claimed in claim 20 wherein thematerial is shredded into strips of about 10 to 20 mm in width.
 22. Amethod as claimed in claim 21 wherein the strips are shredded so as tohave rough edges which interlock when compressed.
 23. A method asclaimed in claim 20 wherein the shredded material is washed and driedprior to being supplied to the chamber.
 24. A method as claimed in claim17 wherein the thermoplastics material is waste plastics.
 25. A methodas claimed in claim 24 wherein the thermoplastics material is a mixtureof different types of waste plastics.
 26. A method as claimed in claim24 wherein the thermoplastics material includes PETE and/orpolyethylene.
 27. A method as claimed in claim 24 wherein the materialto be formed includes at least one of sawdust, wood chip, fiber andpaper.
 28. A method as claimed in claim 17 wherein the article is cooledby supplying cooling fluid to the chamber prior to releasing the articlefrom the chamber.
 29. A method as claimed in claim 17 wherein thearticle is cooled by introducing air into the chamber prior to releasingthe article from the chamber.
 30. A method as claimed in claim 17wherein the article is cooled by releasing it from the chamber into afluid bath.
 31. A method as claimed in claim 17 wherein the superheatedsteam is supplied to the chamber via openings provided in one or moreside wall of the chamber.
 32. A method as claimed in claim 17 whereinthe superheated steam is supplied by inserting tubes into the chamberhaving apertures along their length for delivering superheated steaminto the chamber at locations such as to ensure sufficientthermoplastics materials is melted throughout the article to bind thearticle together when it cools.
 33. A method as claimed in claim 17wherein superheated steam at a temperature between 200° C. to 400° C. issupplied to the chamber in step iii.
 34. A method as claimed in claim 33wherein the superheated steam is at a temperature of between 260° C. to320° C.
 35. A method as claimed in claim 33 wherein the superheatedsteam is at a temperature between 280° C. to 300° C.
 36. A method asclaimed in claim 1 wherein a pressure of between 5 psi to 100 psi ismaintained within the chamber during step iii.
 37. A method as claimedin claim 36 where the pressure is maintained at between 5 to 60 psi. 38.A method as claimed in claim 36 when the pressure is maintained atbetween 10 to 20 psi.
 39. A method as claimed in claim 17 whereinsuperheated steam is supplied into the chamber in step iii for a periodof between 10 seconds to 5 minutes.
 40. A method as claimed in claim 39wherein the period is between 10 to 60 seconds.
 41. A method as claimedin claim 39 wherein the period is between 10 to 20 seconds.
 42. A methodas claimed in claim 17 wherein superheated steam at a temperature ofbetween 260° C. to 320° C. is supplied to the chamber for a period ofbetween 10 to 20 seconds at a pressure of between 5 to 25 psi.
 43. Amethod as claimed in claim 17 wherein superheated steam at a temperatureof about 300° C. is supplied to the chamber for a period of about 15seconds at a pressure of between 5 to 25 psi.
 44. A method as claimed inclaim 17 wherein superheated steam at a temperature of about 300° C. issupplied into the chamber for a period of between 10 to 15 seconds and apressure of about 15 psi is maintained in the chamber.
 45. A method asclaimed in claim 1 wherein the material is reduced in volume by a factorof between 5:1 to 25:1.
 46. A method as claimed in claim 45 wherein thematerial is reduced in volume by a factor of between 10:1 to 20:1.
 47. Amethod as claimed claim 1 wherein the material includes up to 20% ofmaterial that is not thermoplastic material.
 48. A method as claimed inclaim 1 wherein the material includes up to 10% of material that is notthermoplastic material.
 49. A method as claimed in claim 2 wherein thematerial is compressed by substantially the same amount in eachdirection of compression.